Seaplanes are aircraft that are capable of taking off and landing upon water. Seaplanes may fall into two broad categories. In the first category, the lower part of the fuselage is shaped like a boat hull and which, at rest and at low speeds, floats on the surface like a boat. The second category consists of conventional land planes that are mounted on floats in place of, or in addition to, conventional landing gear, which are often referred to as float planes.
A seaplane that is also equipped with wheels is called an amphibian: an airplane capable of operating on land or water. An amphibian aircraft is designed to operate on unimproved runways and water and is an effective form of transportation into remote and undeveloped areas. Amphibians typically include a pair of floats with landing gear that can be retractable or nonretractable. For operating on land, amphibians may include a conventional landing gear design having a pair of main wheels and a tailwheel. This type of landing gear may be preferable for amphibians operating in remote areas because this type of landing gear can be better for unimproved field operation. Other types of amphibians utilize a tricycle landing gear design, also known as a “nosewheel” type of landing gear, which includes a pair of main wheels located on each side of a centerline behind the plane's center of gravity, with a nosewheel mounted on centerline forward.
For operating on water, float planes and amphibians typically utilize a float shape that stabilizes the aircraft in water, yet does not significantly impede the aircraft's performance in the air. Earlier float designs tended to rely more heavily on displacement than planing at higher speeds, thus to some extent impeding takeoff ability. One answer to this problem included providing a step so that at higher speed on the water, the wetted surface of the float was lower, and more forward. A conventional float shape is often described as a planing tail because it only has one step with a forebody ahead of the step and an afterbody behind the step and a V-shaped bottom surface to reduce water impact loads. Many conventional float designs place the step at approximately the same position as one would mount the main landing gear.
The location of the main landing gear for land-based aircraft, and consequently the conventional location of the step for aircrafts, is determined on factors that include location of the most aft center of gravity (“c.g.”). For example, in the tricycle landing gear design, the landing gear main wheels are positioned behind the c.g. so that at relevant portions of the aircraft performance envelope, the center of gravity remains ahead of the main wheel contact point. Additionally, the main gear can be disposed at a trailing angle relative to the ground to give the aircraft inherent dynamic stability on the ground. In some cases, the main gear can be located at a trailing angle measured from a vertical line passing through the c.g. or near the c.g. This angle can range from 5° to 7° or more for some designs, for example, but may be higher or lower depending on a number of factors.
For amphibians with retractable landing gear, the location of the step at approximately the same position as one would mount the main landing gear causes the main landing gear to be located further aft than the desired location described above. A further aft main landing gear position may result in longer takeoff runs or more abrupt takeoffs on land because the further aft position of the landing gear makes it more difficult to rotate the aircraft on takeoff. The greater difficulty in maneuverability is due in part to the longer distance between the main landing gear and the c.g., which results in a higher moment needed for rotation, in turn requiring more elevator deflection, more airspeed, or both, before the aircraft can be rotated to the proper angle of attack for lift-off.
Locating the step in the conventional location for the main wheels also introduces negative handling characteristics on water that require constant pilot input after touchdown because the float plane or amphibian is balancing on the floats until the floats transition from planing mode to displacement mode. In effect, handling a float plane or amphibian with a conventionally located step after touchdown can be described as analogous to balancing a broomstick on one's fingertips.
In some instances, seaplanes may also land and takeoff from surfaces such as snow, wet grass, marshy areas or other unimproved surfaces. In an emergency, these planes may be required to land and takeoff on soil or even pavement. In these situations, the conventional V-shaped bottom has a tendency to dig into the surface, impeding the ability of the aircraft to separate from the surface on which it is moving.
Typically, smaller seaplanes include a propeller power plant that is either forward- or aft-mounted. Forward-mounted propeller power plants, as known as tractor propellers, have the engine and propeller mounted at the front of the aircraft where the thrust draws or pulls the airplane. Tractor propellers in seaplanes can send excessive spray over the cockpit and are more susceptible to bird collisions in areas that present such a hazard.
Aft-mounted propeller power plants, as known as pusher propellers, feature propellers mounted behind the engine where the thrust produced by the propeller pushes the airplane forward. Pusher propellers can offer better visibility and less drag than tractor configurations, but tend to reduce wing lift at the higher angles of attack associated with short-field takeoff, as well as during abrupt power corrections in the approach or landing configuration. Typically, maintenance concerns have favored tractor propellers because pusher propellers are subject to damage from turbulent flow, materials coming from the cabin, loose hardware left inside the cowling, and debris thrown up by the landing gear.
In either configuration, open-design propellers create a substantial amount of noise and can be less efficient than propellers rotating within a shroud, which reduce tip effect loss.
Accordingly, there is a need for a seaplane or amphibious design that improves the location of the step and landing gear for improved handling during takeoff and landing on both land and water. There is also a need to provide a float shape that enables efficient separation of the aircraft from the water and allows the aircraft greater flexibility to takeoff and land on a variety of surfaces. Moreover, there is a need for a seaplane or amphibious aircraft design featuring a shrouded pusher propeller power plant design with improved visibility, less drag, improved thrust performance at static and low speeds for short-field takeoffs, reduced likelihood of damage during operation, and quieter operation.